Carbon
nanohorn is a new allotrope of carbon found in recent years. It can be seen as
a single layer of graphite, one end is an angular closed structure and the
other end is an open structure. The diameter of the carbon nanowires is
generally from 2 to 5 nanometers and the length is from several nanometers to
tens of nanometers. The carbon nanowires usually aggregate into spherical
aggregates of 50-100 nanometers in diameter, with one end of the pyramid
pointing to the outside of the aggregate. The pyramidal hollow structure and
the unique morphology of carbon nanohorn have great potential in catalyst
carrier, fuel cell, lithium ion battery and drug transport carrier. Therefore,
the synthesis and characterization of carbon nanohorn have become a hotspot in
scientific research recent years.
Carbon
nanohorns CNHs have various important applications as below:
(1)
Adsorption and storage materials
CNHs
have a large specific surface area and high binding energy, can be used as a
new type of adsorption materials, such as adsorption gas xenon and hydrogen,
CNHs have two kinds of adsorption sites: the gap between the angle and the
angle of the gap. The use of nitric acid to treat CNHs can increase the pore
volume of the interior and the gap significantly and can be used to store
supercritical methane. In addition, CNHs can also be used to adsorb liquids
such as water, benzene and ethanol.
(2)
Catalyst carrier
Unique
structure of CNHs can enhance the durability of the catalyst. The Pd-CNHs can
obtain the Pd-CNHs with an average size of 2.3 nm, and the gas phase reaction
of H2-O2 and some liquid reaction, such as coupling reaction, which have good
catalytic ability. The particle size of Pt particles synthesized by CNHs is
only about 2 nm, and it has good dispersibility. Pt-CNHs as the electrode of
fuel cell have very good activity and stability.
(3)
Drug carrier
CNHs
have a large specific surface area and numerous angular voids that can adsorb
large amounts of molecules. Compared with CNTs, SWCNHs have smaller pore size
and are suitable for adsorption of relatively small molecules. CNHs do not use
metal catalysts to avoid cytotoxicity caused by metal impurities. CNHs are
assembled into micron-like bundles or form spherical aggregates that enhance
the permeability and retention of drugs under passive tumor targeting
conditions, and tend to be enriched near tumor tissue to provide a higher
resistance to tumor.
(4)
Electrochemical applications
CNHs
can be used as electrode materials in electrochemical sensors. CNHs modified
glassy carbon electrode on the uric acid, dopamine and ascorbic acid and other
good electrocatalytic performance; CNHs directly grown on the carbon fiber can
be made of independent electrodes for lithium-ion batteries; through the
opening of large size nano-window, CNHs can be built a high-capacitance
supercapacitor in an organic solvent.
(5)
Other applications
Tubular
carbon material can absorb the light in the near infrared region so the cells
can be killed by local photothermal therapy; CNHs and metal oxide composite
materials can also be used for lithium ion battery anode material to improve
the performance of the battery; and CNHs doped MgB2 will have magnetic
properties, making it a new superconducting material.
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